Gas generation means



H. l. BRAUN Sept. 26, 1967 GAS GENERATION MEANS Filed Oct. 1, 1965 TIME (SEC) CURRENT (MA) 60 FIG.5

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w A R B WI. ID M W O H ATTORNEY United States Patent 3,343,921 GAS GENERATION MEANS Howard I. Braun, St. Louis Park, Minn., assignor to Honeywell Inc., Minneapolis, Minn., a corporation of Delaware Filed Oct. 1, 1965, Ser. No. 492,236 6 Claims. (Cl. 23-281) This invention relates generally to gas generating devices and more particularly relates to a carbon dioxide generator in which a pellet of solid propellant material is ignited by means of passing a small electrical current through the pellet.

This invention provides an improved gas generator of the type generally disclosed in the co-pending application of Brenny et al. Ser. No. 486,168, filed Sept. 9, 1965, also assigned to the applicants assignee. The Brenny application discloses a timing device in which a pellet of propellant material is ignited in a closed chamber to produce a high pressure carbon dioxide gas. The carbon dioxide gas is metered through an orifice assembly at a controlled rate to define a timed period. The pellet in the co-pending application was ignited by utilizing a bridge wire that would heat the pellet to a high temperature when a current source was connected to the bridge wire.

The invention herein provides a new system for igniting the pellet that is used in the timing device of the co-pending application. Instead of applying heat by means of a bridge wire to ignite the pellet, a pair of electrodes are connected across the pellet. A low current is applied that, after a certain period of time, causes a chemical reaction in the pellet to give off the carbon dioxide gas in the desired manner. When a bridge wire is used to heat the pellet to ignite it, a current of approximately 30 or 40 amperes is necessary to provide sufficient heat. In the present invention, approximately 60 to 80 milliamps applied to the electrode will ignite the pellet. This large reduction in the current requirement means that a much smaller power supply can be utilized. This reduction in the size of the power supply is extremely important in those applications in which a self sufficient source of power must be packaged with the system.

It is therefore a primary object of the present invention to provide a novel gas generating system in which a pellet of solid propellant material is ignited by the direct application of an extremely low current.

Other objects of the invention will be apparent from the following description of the invention taken in connection with the accompanying drawings in which:

FIGURE 1 is a schematic of the gas generating system;

FIGURE 2 is a cut-away view of a mold that can be used to manufacture the pellet;

FIGURE 3 is a sectional side view of the pellet showing one method of connecting the electrodes;

FIGURE 4 is a sectional perspective view of the pellet disclosing another method of connecting the electrodes; and

FIGURE 5 is a graph of the current requirements versus time that is required to ignite a typical pellet.

Referring now to FIGURE 1, there is disclosed a schematic diagram of my invention. The system includes a pellet of solid propellant material that when ignited will liberate carbon dioxide gas. The composition of pellet 10 will be discussed in some detail at a later point in the specification.

In the preferred embodiment of the invention pellet 10 is in the form of a right circular cylinder having a longitudinal axis 11. A pair of electrodes 12 and 13 are connected to pellet 10 on generally opposite sides thereof and generally perpendicular to axis 11. Electrodes 12 and Patented Sept. 26, 1967 13 are connected in any manner that will assure intimate contact with the material in pellet 10.

Connected in series with electrodes 12 and 13 across pellet 10 are a power supply 14, a normally open switch 15, and a current limiting resistor 16. When switch 15 is closed, power supply 14 provides a current flow through switch 15, resistor 16, electrode 13, pellet 10, electrode 12, and back to current source 14. It is noted at this point that electrodes 12 and 13 are located so that current flowing through pellet 10 flows in a direction generally perpendicular to axis 11.

Referring noW to FIGURE 2, there is disclosed a cross sectional view of a mold that can be used to manufacture pellet 10. A steel mold can be used to manufacture pellet 10. A steel mold 20 can be used to compress pellet 10. Mold 20 has a cylindrical central opening having one end open and the other end closed except for a small opening 21 that is used to remove the material in the mold after compaction. Inserted within the mold 20 is a first metal slug 22 having the same cross sectional dimensions as the mold chamber. The material of pellet 10 is poured on top of slug 22. A second metal slug 23 is then placed on top of pellet 10 and pressure is applied. When high pressure is applied to slug 23, the desired pellet 10 is formed. 'After the pellet is formed, slug 23 can be removed and then slug 22 is forced from the chamber to remove pellet 10. The particular type of mold or die that is used to manufacture pellet 10 is not critical to the invention. Other types will be known to those skilled in the art.

The pressure mold 20 is applied in parallel with axis 11 of pellet 10. It is important that the direction of compaction of the pellet is known, since the electrodes must be connected normal to this direction'to cause proper ignition. Numerous tests were conducted with the system disclosed in FIGURE 1 to determine the proper connection of the electrodes. It was found that reliable and repeatable results could be obtained only when the leads were aligned normal to the direction of compaction, that is normal to axis 11 in FIGURES 1 and 2. When the electrodes were connected in parallel with the direction of compaction, the current tended to follow a short path on the outside surface of the pellet and ignition did not occur.

Pellet 10 is basically a compacted mixture of silver carbonate and elemental carbon. The pellet can be prepared as follows. Ten parts of AR. grade silver carbonate powder are mixed with one part of NF grade charcoal powder in a mortar. The powders are ground together as thoroughly as possible. Five grams of this powder mixture are then dissolved in a slurry made with concentrated ammonium hydroxide. The silver carbonate is thus dissolved in the ammonium hydroxide. This slurry is then evaporated to dryness at a 150 F. This procedure thoroughly coats the carbon particles with silver carbo nate. A pestle is then used to again grind the sample in the mortar. This powder is then mixed with a sufficient amount of a 20% ammonium hydroxide solution to make a thick paste. The paste is then placed in a mold and subjected to 7000 p.s.i. for 5 minutes. The pellet is then removed and dried for several hours at 150 F. This procedure yields a smooth solid pellet that does not easily fracture.

A simple form of electrode attachment is disclosed in FIGURE 3. Pellet 10 is mounted on a base 25. Electrodes 12 and 13 are mounted in holding devices 26 and and 13 to assure intimate contact. In simplest form, electrodes 12 and 13 can be nicrome wires that are forced into the sides of the pellet.

Another method of attaching electrodes 12 and 13 is disclosed in FIGURE 4. In this case, the electrodes are actually imbedded in a pellet. This can be done by drilling holes in the pellet and inserting the electrodes or, if a special mold is used, the electrodes can be molded directly in the pellet.

The mechanism of ignition is as follows. The pellet in its original form exhibits a resistance of approximately 20,000 ohms per inch normal to axis 11. In the system disclosed in FIGURE 1, pellet 10 thus acts as an extremely high resistance to current flow. In the preferred embodiment of the invention, power supply 14 provides approximately 20 volts. When this voltage is applied across electrodes 12 and 13, an extremely small amount of current begins to flow through pellet 10. The carbon in the pellet acts as a conductor. Because of its high resistance, pellet 10 begins to heat when current is applied. The heat caused by the flow of current causes a chemical reaction to occur that results in the liberation of carbon dioxide gas and the formation of pure silver. Some residual carbon also remains. The reactions that occur are as follows:

(Heat) (Heat) The heat caused by the flow of current causes the reaction to begin. The reaction, once it begins, is exothermic. The heat produced by exothermic reaction (1) is then used to carry out reaction (2). The heat provided by the fiow of current decreases quickly once reaction (1) begins since the resistance of pellet 10 decreases.

From the above equations, it can be seen that the heat causes the silver carbonate to decompose to form silver oxide and carbon dioxide gas. The silver oxide then combines with the carbon when heat is added to form pure silver and additional carbon dioxide gas. After the reaction is complete, the resistance of pellet 10 is on the order of 1 ohm per inch. The purpose of current limiter 16 is therefore to prevent damage to the power supply after pellet 10 has been expended.

FIGURE discloses a graph of the current requirements versus time to ignite a typical pellet. The pellet used to obtain the results shown in FIGURE 5 was approximately .1 inch thick by .25 inch in diameter. The electrodes were connected as shown in FIGURE 3. This pellet exhibited a resistance of approximately 7000 ohms when connected as shown in FIGURE 1. A DC voltage supply provided 31 volts and a current limiting resistor of 60 ohms was used. It can be seen from FIGURE 5 that this combination provided ignition after approximately 700 seconds when the current reached 65 milliamps.

In another test, a 31 volt power supply was used with a pellet having a resistance fo 4.4K ohms. In this test the pellet ignited at a current level of 65 milliamps after only 36 seconds.

In another test 20.5 volt DC source was used with a K ohm pellet. Ignition occurred at 60 milliamps after 2736 seconds.

The voltage supply can thus be changed to vary the delay between the time the voltage is applied and ignition occurs. For faster ignition, a higher voltage source can be used. With regard to the voltage supply, it is important that the contact resistance between the electrodes and the pellet be made as small as possible so that the voltage is not dissipated in contact resistance.

Tests were also conducted to determine the temperature range over which the pellets could be ignited. It was found that pellets could be ignited at any temperature in the range of 65 F. to 160 F.

For comparison purposes, tests were run in which the pellets were ignited by means of a bridge wire mounted adjacent to the pellet. The current through the bridge wire required to ignite the pellet was found to vary from 30 to 47 amperes when using a power supply of 20 volts DC. Opposed to this are the findings of tests conducted with the present invention. By using the teachings of the present invention, the pellets were found to ignite when from 60 to milliamps were applied.

It is noted that in addition to providing a gas generating function, my invention inherently provides a time delay. The time required for ignition can be varied as disclosed above by varying the voltage and other parameters in the system. This system can therefore be used as a time delay device as well as a gas generator.

Other variations will occur to those skilled in the art. Although the pellet is shown in cylindrical form in the preferred embodiment, it should be obvious that other forms can be utilized, if desired. Neither is the exact method of preparing the pellet critical to the invention. For these reasons, I intend to be bound only by the scope of the appended claims.

What I claim is:

1. A carbon dioxide generator, comprising:

(a) a right circular cylindrical pellet of solid propellent material, said material being a mixture of silver carbonate and elemental carbon that is compressed into a dense pellet by pressure applied in parallel with the longitudinal axis of said cylindrical pellet, said pellet exhibiting a high resistance to the flow of an electric current in a direction normal to said axis;

(b) a pair of electrodes mounted adjacent the sides of said pellet, said electrodes being aligned normal to said axis to make contact with said pellet on opposite sides thereof so that a current flowing between said electrodes flows normal to said axis; and

(c) circuit means including a low voltage source of power, a switch, and a current limiting device connected in series across said electrodes to provide a small flow of current through said pellet when said switch is closed to react said silver carbonate and carbon to form carbon dioxide gas and free silver, said free silver making the residue of said pellet highly conductive.

2. A carbon dioxide generator, comprising:

(a) a pellet normally exhibiting a relatively high resistance to the flow of electric current, said p'ellet comprising a compacted mixture of silver carbonate and carbon;

(b) a pair of electrodes connected on opposite sides of said pellet so that a current flowing between said electrodes flows normal to the direction of compaction of said pellet; and

(c) circuit means including a source of power, switching means and current limiting means connected in series across said pair of electrodes to provide a small flow of current across said pellet when said switch is closed to thereby initiate the following reaction:

(Heat) AgrCOa AgzO COzT(gas) A (Heat) 2Agz0 O 4Ag comets 3. A carbon dioxide generator, comprising:

(a) a densely compacted pellet normally exhibiting a relatively high resistance to the flow of electric current in a diretcion normal to the direction of compaction, said pellet comprising a mixture of silver carbonate and elemental carbon;

(b) a pair of electrodes connected to said pellet so' that a current flowing between said electrodes flows normal to the direction of compaction; and

(c) circuit means including a source of power, switch means and current limiting means connected in series across said pellet when said switch is closed to thereby initiate a chemical reaction to form carbon dioxide and free silver.

4. A gas generator, comprising:

(a) a cylindrical pellet of solid propellent material, said material being a mixture of silver carbonate and carbon that is compressed into a dense pellet by pressure applied in parallel with the longitudinal axis of said cylindrical pellet, said pellet normally exhibiting a high resistance to the flow of an electric current in a direction normal to said axis; and

(b) a pair of electrodes mounted in intimate contact with said pellet and on generally opposite sides thereof so that a current flowing between said electrodes flows normal to said axis to decompose said silver carbonate to form carbon dioxide gas.

5. Apparatus of the class described, comprising:

(a) a generally cylindrical pellet normally exhibiting high resistance to the flow of electric current, said pellet comprising a compacted mixture of silver carbonate and an electrically conductive binder material;

(b) a pair of metal electrodes mounted in intimate contact with said mixture, said electrodes being positioned on generally opposite sides of said pellet so that a current flowing between said electrodes flows substantially normal to the direction of compaction of said pellet; and

(c) means for impressing a voltage across said electrodes to establish a small flow of current across said pellet to heat said pellet and thereby decompose said silver carbonate.

6. Apparatus of the class described, comprising:

(a) a pellet of densely compacted silver carbonate and carbon, said pellet exhibiting a high resistance to the flow of an electric current in a direction normal to said direction of compaction; and

(b) first and second electrode means mounted in intimate contact with said pellet so that a small current flowing between said electrodes flows normal to the direction of compaction to heat said pellet to react said silver carbonate to form carbon dioxide gas.

NO references ClteO.

JOSEPH SCOVRONEK, Acting Primary Examiner.

J. H. TAYMAN, Assistant Examiner. 

1. A CARBON DIOXIDE GENERATOR, COMPRISING: (A) A RIGHT CIRCULAR CYLINDRICAL PELLET OF SOLID PROPELLENT MATERIAL, SAID MATERIAL BEING A MIXTURE OF SILVER CARBONATE AND ELEMENTAL CARBON THAT IS COMPRESSED INTO A DENSE PELLET BY PRESSURE APPLIED IN PARALLEL WITH THE LONGTIUDINAL AXIS OF SAID CYLINDRICAL PELLET, SAID PELLET EXHIBITING A HIGH RESISTANCE TO THE FLOW OF AN ELECTRIC CURRENT IN A DIRECTION NORMAL TO SAID AXIS; (B) A PAIR OF ELECTRODE MOUNTED ADAJACENT THE SIDES OF SAID PELLET, SAID ELECTRODES BEING ALIGNED NORMAL TO SAID AXIS TO MAKE CONTACT WITH SAID PELLET ON OPPOSITE SIDES THEREOF SO THAT A CURRENT FLOWING BETWEEN SAID ELECTRODES FLOWS NORMAL TO SAID AXIS; AND 